Method of and apparatus for making printing plates



March 8, 1938. .J. SCHWARTZ ET AL METHOD OF AND APPARATUS FOR MAKING PRINTING PLATE Original Filed Jan. 13, 1932 Semi/art 13 m m w m lamp]; BY

TORNEYS.

Patented Mar. 8, 1938 UNITED STATES k PATENT OFFICE METHOD OF ANDAPPARATUS FOB MAKIN PRINTING PLATES Joseph Schwartz, Philadelphia, 1a., and Amos Acklcy, Camden, Thomson, Inc., 1' of Pennsylvania 1., asaignors to Wcstcott d: elphia, Pa, a corporation Continuation of application Serial no. 586,264,

January 13, 1932. 1936, Serial N0.- 16,674

(3 Claims.

molten material or type metal, to avoidthe necessity for shaving or trimming the back of the printing plate, and to provide a-printing plate with printing characters having sharp outlines 10 and a. solid body. In accordance with our invention, we suck out of the molten metal, through porous surfaces at one or both sides of the mold used for casting the plate, the gas bubbles forming, segregating, or otherwise entrapped in the 15 metal, thus preventing the formation of blow holes in the plate and improving its solidity, strength, and sharpness of printing characters. Other features and advantages of the invention will appear from the following description of a species or form of embodiment, and from the drawing. i I

. This application is a continuation 'of our pending application Serial No. 586,264, filed January 1 -13, 1932, as to common subject matter.

In carrying out our invention as here illustrated and as described in detail hereinafter, the molten type metal for forming a printing plate is poured between a front matrix or intaglio sheet .and a heat insulating backing sheet spaced therefrom and preferably formed of fibrous material. Thesednner matrix and insulating sheets are suitably positioned realtively to one another by the bed or front plate and cover or back plate of a casting born-against which plates the 'matrix and insulating sheets may be firmly and uniformly held as a result of the suction or ex-' haustion of-air through a multiplicity of small apertures formed in such plates} and covered by the matrlx'and insulating sheets. By sufliciently 40 energetic suction through the perforated or 'foraminous plate(s) as just described, bubbles of gas inthe molten material, which might otherwise remain entrapped-therein and form blowholes in the solidified printing plate, are sucked 45, out through either or both of said sheets, which line the aforesaid foraminous wall structure of the mold,eithe'r or both be ingof suillciently .permeableor porous character. In many cases. it is desirable to make the matrix sheet of close- 5o textured, relatively impermeable pressed paper stock, and to draw or suck off. the gases mainly v through a more porous backing sheet. The front and back plates are preferably provided with unpolished or frictional surfaces so t ere can 5 be no slip e of the matrix or insulating sheet purpose. To draw oil gas bubbles through such matrix hereinbefore referred to.)

, ally without sudden and unequal chilling of, difthe metal are sucked This application April 27,

relatively to the plates, and suctiomis so uniformly applied to the backs of the matrix and the insulating sheet as to hold them against wrinkling or contraction as a result of contact oi. the liquefied type metal therewith or of the cooling of such metal. The sheets are held by suction at so many different points that the stresses are uniformly distributed throughout the entire area -of the sheets, without any tendency. to tearing. The insulating backin'g sheet is preferab composed of fibrous material, such asv paper,

which is incombustible at the melting point of type metal, has a smooth surface, and is of sufficient porosity. Thus the surface of the cooling type metal has little or no tendency to slip thereon. No. 1 jute paper about 10/1000 in. thick has been found very satisfactory, though any stout paper such -as above indicated will answer the a sheet effectively, a degree of suction or partial vacuum materially in excess of what would be necessary merely to hold the sheet firmly in place is needful: e. g., a partial vacuum corresponding to some 7-15 in. of mercury,-l0 in. representing a fair mean,as against a mere 1 M2 in. suction,

- required to hold a sheet against the mold plate.

The insulating sheet such as above indicated characteristics similar to that of the matrix or intaglio sheet when the latteris composed of a plastic porous pulp or paper sheet having char-' acters impressed therein, and then hardened. (This is more porous thanthe dense-pressed By'using' insulating sheets of different thicknesses, printing plates of different thicknesses may be cast from the same matrix, or from matrices of like thickmesses. o

In carrying out our invention in casting a printing plate, the molten type metal is pouredbetween parallel walls, consisting of the matrix and insulating sheets, which have substantially the same temperature and characteristics, and hence. the type metal is permitted, to cool natur- 5 '4 ferent surfaces or parts thereohand the bubbles of gas or air which are entrapped or formed in ut. Since the matrix and. insulating sheets are held by the suction firmly,

and without wrinkling, contracting, or tearing,

"against the frictional surfaces of the apertured plates, the usual shrinkage of the printing plate in cooling is minimized. The back of the printing plate has a, smooth, uniform surface, suitable for use without shaving. The exhaustion of air prevents any air being trapped in the intaglio In the drawing, Fig. I is a front elevation of for the practice of our improved method. I

Fig. I! is a top plan view of the casting box with the cover open.

Fig. m is a top plan view of the casting box with the cover closed; and

enlarged scale taken through the bed, matrix, plate of type metal, insulating sheet, and cover, in the plane indicated by the line IV-IV of Fig. III.

In the embodiment of our apparatus illustrated in the drawing. a supporting base I has fixed thereto a plate I forming an end closure for a hollow casting box 3 provided with a concave wall 4 adapted to form a bed or front. The lower unpolished portion of the wall 4, adapted to form a frictional seat for a matrix 5, is provided with numerous, apertures or perforations. preferably of small cross section and comparatively closely spaced. and communicating with the suction chamber 1 of the box I. The suction chamber 1 communicates through a suitable tube with the exhaust side of apump I, which may be driven from any suitable source of power, such as the electric motor ll. The operation of the 'Lwhichresultsinthematrixlbeingheldata against the surface of the bed by atmospheric presure.

Adoororclosure ll ishingedtothe casting box I and has an unpolished convex wall it forming formedbythewalllandhavingatapemdtopli providingamouth for receivingthecastingmetal whenthedoororbackllisclosed.

Thewall l2 contains apertures preferably o1 small cross section and closely chamber liinthecover ll. Thechamber ll comnumicatesthroughatubellwiththeexhaust sideofthepump0,t1 1e operation ofwhich causes 'iheccvermaybeheldindesiredclosedrelationflaiptotheboxbyalatchilonthebox coactingwithabomorstudlionthecover."

bythe pumpl from thechambers I ll; thematrixlissatedintheboxwithits characters by the rising metal. The characters are sharp in outline and free from blow holes.

apparatus embodying our invention and adapted l'lg. IV is a transverse sectional view on an exhaust pump creates a vacuum in thechamber'.

great number of points securely and uniformly a frictional core complementary to the bed ll, which are spaced and which communicate with the vacuum through the foraminous wall structure In accordance with our invention, theair is plate.

through the matrix (whenthe latter-is sufficient,

tween the tapered surface ll and-the upper un-i 1y porom), as well as through the backingsheetf,

perforated portion of the concave wall of the casting box; the suction on the matrix and insulating sheet being meanwhile maintained.

' The type metal flows downward between the matrix 5 and insulating sheet II to form a printing plate ",which cools and hardens gradually-and uniformly due to the similarity of temperature and characteristios of the surfaces of the matrix and sheet with which it contacts. The matrix and insulating sheet are prevented from slipping .or shrinking by the suction uniformly applied to their back surfaces,'and resist or minimize the shrinkage of the printing plate 20 during cooling, since the metal interlocks with the intaglio recesses of the matrix and in the pores and on the filaments of the insulating sheet, which is prevented from tearing or wrinkling by the uni.-

form distribution over the entire area thereof of the stresses communicated thereto. As alrea y mentioned, gases are drawn out of the molten metal through one or both of the sheets I and I1, preventing the formation of blow holes and assuring a solid, uniform structure of the metal when solidified. When the inner (matrix and backing) sheets I, II are removed from the mold box along with the cast printing plate II, air drawn through the holes 8 and I4 by the exhaust pump 8 serves to cool the mold walls 4 and I2, until the sheets I, II are replaced, or the pump a is stopped.

Plates can be cast as thin as would normally be desired without risk of having blow holes therein, and of unvaryins standard thickness, so that the usual shaving of their back is unnecessary.

Having thus described our invention, we claim:

1. An improved methodof casting a printing plate in a mold comprising front and back walls, with a porous inner. sheet lining at least one of said walls and in contact with the molten plate ,materialwhenthelatterispouredinthemoid;

, walls, at least one of them foraminous, a porous inner sheet lining for the said foraminous wall structure of said mold, and means for exerting, and the said porous sheet lining, a suction suiiicient to draw oil through said lining the gas bubbles in the molten plate material poured in the mold. thereby preventing the formation of blow holes and assuring aselid. uniform structure of the cast coma scnwaa'rz.

A1108 ACKLEY.

sheet lining aforemen- 

